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Wednesday, June 13, 2012

Class XI, BIOLOGY, "Kingdom Monera"

BACTERIADISCOVERY
Bacteria was discovered by A.V. Leuwenhoek in 1676.STRUCTURE OF BACTERIA
Bacteria are smallest and simplest living organism measures from 0.2m
to 2 micron in breadth and 2 to 10 micron in length. They are strictly
unicellular but some species remain associated with each other after
cell division and form colonies.
A generalized bacterial cell consists of following structures.(1)FLAGELLA
They are extremely thin appendages, which originate from basal body, a
structure in the cytoplasm beneath cell membrane. Flagella help in
bacterial locomotion.(2)PILLI
They are hollow, filamentous flagella like appendages, which help in conjugation but not in locomotion.(3)CAPSULE
It is a protective sheath made up of polysaccharides and proteins. It
provides greater pathogenicity and protects bacteria against
phagocytosis.(4) CELL WALL
Bacterial cell wall mostly made up of amino acids, sugar and chitin. It
surrounds the cell membrane, determine shape and protects bacteria from
osmotic lyses. Most bacteria have a unique macromolecule called
Peptidoglycan in addition to it. Sugar molecules, teichoic acid, glyco
proteins and lipo polysaccharide are also present.(5)CELL MEMBRANE

It is present inside the cell wall attached to it at few places containing many pores.

It is made up of lipids and proteins.

It acts as a respiratory structure.

(6)CYTOPLASM
Bacterial cytoplasm is granular containing many small vacuoles, glycogen particles and ribosomes.(7)MESOSOMES

These are the invaginations of the cell membrane into the cytoplasm.

They are in the form of vesicles, tubules or lamella.

They help in the DNA replication, cell division, respiration and export of enzyme.

(8)BACTERIAL HEREDITARY MATERIAL

Bacterial hereditary material DNA is found as concentrated
structures called Bacterial chromosomes or chromatin bodies. It is
mostly scattered in the cytoplasm.

A small fragment of extra chromosomal circular DNA, called Plasmid is also present.

FIGURE 6.1 (FROM TEXT BOOK)CLASSIFICATION OF BACTERIAON THE BASIS OF SHAPE
On the basis of shape bacteria can be divided into four categories.(1)COCCI

These are spherical or rounded bacteria presents in the form of mono, diplo or streptococcus form.

They are non-flagellated and cannot move from one place to another place.

FIGURE (FROM TEXT BOOK)(2)BACILLI

Bacilli are rod shaped bacteria, can be present in the form of diplo or streplobacilli.

They may be flagellated and can move from one place to another.

FIGURE (FROM TEXT BOOK)(3)SPIRILLA

These are spiral or cork, screw shape bacteria also known as spirochetes.

It includes chlamydia and rekettia.

FIGURE (FROM TEXT BOOK)(4)VIBRIO OR COMMA

These are slightly curved bacteria like vibrio cholera.

They may be flagellated and can move.

ON THE BASIS OF RESPIRATION
On the basis of respiration bacteria can be divided into two main types.(1)AEROBES
Require oxygen for respiration.(2)ANAEROBES
Respire with out oxygen
Sub-classes of this classification are as follow:(A)FACULTATIVE BACTERIA
Respire with or without oxygen.(B)MICRO AEROPHILIC BACTERIA
Require low concentration of oxygen for growth(C)OBLIGATE ANAEROBES
These bacteria only survive in absence of oxygen.(D)FACULTATIVE ANAEROBES
These bacteria use oxygen but can respire with out it .(E)OBLIGATE AEROBES
These bacteria only survive in the presence of oxygen.ON THE BASIS OF NUTRITION
Bacteria can be divided into four main types on the basis of nutrition. Which are as follow.(1)SAPROTROPHIC BACTERIA

These bacteria depend on the dead organic matter for their nutrition.

They are mostly present in the humus of soil and posses large number
of enzymes that convert complex substances of humus to simpler
compounds.

(2)SYMBIOTIC BACTERIA

These bacteria are found associated with other living organism.

They obtain their food from the host without harming it. E.g.
Rizobium redicicola (Symbionts in the root nodules of pea family
plants).

These bacteria can sythesize organic compound from simple inorganic substances.

Autotrophic bacteria can be divided into photosynthetic or chemosynthetic.(A)PHOTOSYNTHETIC

These bacteria contain green pigment chlorophyll, which is known as bacterial chlorophyll, or chlorobium chlorophyll.

These pigments are present in mesosomes (invagination of the cell membrane in the cytoplasm)

These bacteria utilize H2S during photosynthesis instead of water and liberate sulphur instead of oxygen.

sunlight

(B) CHEMOSYNTHETIC

These bacteria obtain their energy from oxidation of some inorganic
substances like iron, hydrogen, nitrogen and sulphur compounds.

LOCOMOTION IN BACTERIA

Some bacteria can move from one place to another with the help of a wipe like structure flagella.

Flagella allow bacteria to disperse into new habitats, to migrate towards nutrients and to leave unfavorable environment.

Flagellated bacteria show orientation towards various stimuli, a behavior called Taxis.

Some bacteria are chemo tactic, phototectic or magnetotatic.

GROWTH IN BACTERIA
In favorable conditions bacteria can grow, very rapidly. There are
some factors affecting growth of bacteria such as Temperature, nutrient
availability, PH and ion concentration. Bacterial growth can be divided
into four main phases, which are as follows(1)LAG PHASE
It is inactive phase during which bacteria prepare them for division.(2)LOG PHASE
In this phase bacteria grow and multiply very rapidly.(3)STATIONARY PHASE
In this phase bacterial multiplication is equal to bacteria death rate.(4)DECLINE/DEATH PHASE
In this phase death is more rapid then multiplication rate.REPRODUCTION IN BACTERIA
Usually asexual reproduction is present in bacteria which is as followFISSION
Fission is the fastest mode of bacterial asexual reproduction (Binary Fission)

It usually takes place in favorable conditions.

Hereditary material DNA in the form of chromatin body replicates.

After the replication of hereditary material a constriction appears
in the middle of the cell, which later splits it into two parts.

Newly form bacterial cells grow in size and form nature bacterial cells.

The single fission takes place in 20-30 minutes.

ENDOSPORE FORMATION

It is the method of bacterial survival under unfavorable conditions. Following are the main characters of this process.

During this process, the whole protoplasmic content gets shrink into a small mass.

A cyst is formed inside the parental wall around constricted protoplasm to form endospore.

On the return of favorable conditions parental wall raptures due to decay and endospore is set free.

In the end, this endospore enlarges to form a mature bacterial cell.

FIGURE 6.4 (BINARY FISSION IN BACTERIA)
FIGURE 6.5 (FORMATION OF ENDOSPORE)GENETIC RECOMBINATION IN BACTERIA
Genetic changes with the help of which bacteria adopt new
characteristics (drugs resistance pathogenic ability) is known as
Genetic recombination
Three types of genetic recombination are present in bacteria, which are given as follow.1.CONJUGATION
Simple process of genetic recombination in which genetic material is
transferred from one bacteria to another through a conjugating tube.
Conjugation in bacteria was discovered by Joshua Lederburg and Edward
L.Tatum in 1946EXPERIMENT
J.laderberg and E.Tatum performed an interesting experiment in order to
prove conjugation in bacteria. Following are the main steps of this
experiment.
1. They selected a wild type bacteria (E-coli) and obtain (triple nutritional mutants) different from one another.
2. Wild-type was capable of synthesizing six substances symbolized as A, B, C, D, E and F.
3. Mutant type I was capable of synthesizing three substances symbolized as A, B and C but not D, E and F.
4. Mutant type II was capable of synthesizing three substances D,E and F but not A,B and C.
5. These mutant type I and II were grown together in the growth medium having all the six substances A, B, C, D, E and F.
6. After several hours, three types of bacteria were detected after nutritional test which were,
i. Both mutant I and mutant II types.
ii. Wild type bacteria synthesizing all the six substances.
iii. A new type of bacterial strain requiring all the six substances for growth.
In this experiment, appearance of wild type and one new type is an evidence that conjugation had taken place.2. TRANSDUCTION
It is the mode of genetic recombination in which genetic material is
transferred from one bacteria to another by a third party, which is
usually bacteriophage.
This process was experimentally carried out by Lederberg and Zinder in 1952.EXPERIMENT
1. In this experiment, a bacteriophage is made to attack a bacterium known as “donor” (D).
2. The injected DNA of bacteriophage multiply to form a large number of daughter phages.
3. The donor bacterium (D) gives some of its genetic material “D” to the multiplying particles.
4. The phages released from this donor bacterium contain the genetic
material of phage plus a little piece of the donor genetic material “D”.
5. These new phages then made to attack a new bacterium known as “Recipient” (R).
6. These recipient bacterium is not destroyed like the donor in order to
reproduce normally. In this way, genetic material of the donor
bacterium is carried to the recipient bacterium by a bacteriophage and
this process is known as Transduction.3. TRANSFORMATION
In this process, genetic information transfers from one bacteria to another by producing a change it (undergo a change).
This type of genetic recombination was first proved by Fred Griffith in 1928.EXPERIMENT
Griffithi injected a small quantity of R-type bacteria and a large quantity of heat killed S-type bacteria into the same mouse.
This treatment proved fatal as mouse surprisingly suffered from Pneumonia and died.
The autopsy of the mouse revealed the presence of living S-type bacteria in the mouse in addition to R-type.
From this experiment Griffith concluded that,
The live R-type bacteria had been transformed into live S-type bacteria
due to transfer of some material from dead S-type, cells.
Thus this transformation occurred due to genetic recombination in R-type bacteria.
In his experiment, he had been working on two strains of bacteria
“Pnemococcus”. One strain is known as smooth type (Virulent and causes
Pneumonia) while the second strain is known as (Rough type (Non-Virulent
and does not cause pneumonia).
NOTE: (IMPORTANCE OF BACTERIA (USEFUL AND HARMFUL BACTERIA)FROM BOOK PAGE # 116 (OLD BOOK – 2003)VACCINATIONDEFINITION Inoculation of host with inactive or weaken pathogens or pathogenic products to stimulate protective immunity.

In case of subsequent natural infection with the same pathogen the
immune system easily recognized the invader and comfortably managed to
overcome the pathogen.

A vaccine can taken orally (Polio vaccine) or injected into the body (Tetanus Vaccine).

IMMUNIZATIONDEFINITION It is a process of induction of specific immunity by injecting antigens, antibodies or immune cells.

The protoplasm differentiated into an outer colored region
chromoplasm, which contain various pigments in which chlorophyll “a” and
phycocyanin are more important.

Inner colorless region of the protoplasm is known as centroplasm.

They are mostly aquatic (fresh water)

Sexual reproduction is absent.

Asexual reproduction takes place by means of Harmogonia, zoospores, akinates and fragmentation.

NOSTOC
Nostoc is a typical example of blue green algae.STRUCTURE

Nostoc is a filamentous prokaryotic algae in which filaments are
intermixed in a glatinous mass-forming ball like structure known as
coenobium.

A single filament look like a chain of beads.

Each filament is unbranched and has a single row of rounded or oval cells.

Each cell has double layered wall, outer thick wall is made up of
cellulose mixed up with pectic compounds. While inner thin layer is made
up of cellulose only.

The protoplasm is differentiated into an outer colored region (chromoplasm) and an inner colorless region (centroplasm).

The chromoplasm various pigments like chlorophyll, axanthophylls, carotene, phycocyanin and phycoerythrin.

Ribosome’s, pseudovacuoe and reserve food in the form of cynophyceae starch are present.

Hereditary material is present in cytoplasm with out the nuclear membrane.

In Nostoc filaments slightly larger, colorless cells with thick
walled known as “Heterocyst” are present. The function o Heterocyst is
nitrogen fixation, food storage and multiplication of filament during
unfavorable conditions.

NUTRITION

It is an autotroph and prepares its food in the presence of sunlight.

It also capable of fixing atmospheric nitrogen and converts it into
nitrates in order to prepare amino acids and proteins, this activity
takes place in Heterocysts.

REPRODUCTION

Only asexual reproduction is present which takes place by following methods.

(1)HORMOGONIA

A portion of the filaments between two heterocysts is known as Hormogonia.

During favorable conditions, filaments break up at the junction of each Heterocyst.

The end cells of each homogonous divide to form long filaments of Nostoc.

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